A prior heat exchanger 10 is shown in FIG. 1 fitted to the exterior wall 13 of a wood burning stove 11 for heating of water. The prior heat exchanger 10 includes three extruded aluminum fins 15 each comprising an aluminum plate 16 and an integral, central, longitudinally extending clip 18. The clip 18 comprises a parallel pair of ribs 19 protruding from the exterior face of the plate 16. Fins 15 are fixed longitudinally upright in substantially coplanar relation against the side wall 13 of the stove 11 by screws 21 in through-holes in the stove wall.
The heat exchanger 10 of FIG. 1 further includes a water flow ladder 26 comprising substantially horizontal top and bottom manifolds 28 and 29 joined by upstanding, parallel, rigid copper rung tubes 31-33 snap fitted into the clips 18 of corresponding fins 15. The manifolds 28 and 29 each consist of a pair of conventional copper tees 36 and 37 and a corresponding copper elbow 38 connected by short horizontal rigid copper tubes 41 and 42 in series. The fittings 36, 37 and 38 receive the adjacent ends of the rung tubes 31-33 in the order shown in FIG. 1. The connections of the rigid tubes 31-33, 41 and 42 to fittings 36-38 are individually brazed, the high temperatures possible at the surface of the stove 11 making other forms of connection, such as soldering, unsuitable.
In the FIG. 1 structure, the upper and lower manifolds 28 and 29 must be substantially offset from the ends of the fins 15, by a distance S sufficient to allow for the longitudinal extent of the fittings and brazing material extending from the end of the fitting along the exterior of the corresponding rung tube 31-33. To try to avoid unequal flow rates as between the rung tubes 31-33, which may cause underheating in one rung tube and simultaneous overheating (or even steam production) in the next rung tube, the inlet and outlet copper tubes 51 and 52 lead in opposite horizontal directions from the final fittings 36 of the corresponding upper and lower manifolds 28 and 29. Unfortunately, this results in water line connections at opposite ends of the stove and hence usually in exposure of one or the other of inlet and outlet tubes 51 and 52 at an exposed end of the stove, tending to produce an unsightly appearance.
The plates 16 can be made relatively thin, for example 1/16th inch, to minimize material cost without degradation of heat transfer capability or structural strength for mounting of the water flow ladder to the stove. However, conventional copper tube fittings 36-38, even if quite precisely assembled with their axes substantially in a common plane, tend to bear in line or point contact on the surface of the stove to the extent of lifting the end portions of the fin plates 16 out of best heat conductive relation with the stove wall. The fittings have also been found to restrict water flow where joined to the tubes. The prior heat exchanger 10 has been found unnecessarily limited in the temperature rise thereacross and in some instances to thereby disrupt temperature stratification in a domestic hot water storage tank, to the upper and lower ends of which the outlet 51 and inlet 52 connect.
Accordingly, it is an object of this invention to provide an improved water heating apparatus which overcomes disadvantages of the prior apparatus above discussed with respect to FIG. 1.
Other objects and purposes of this invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings.
The objects and purposes of the invention are met by providing a solid fuel burning stove, furnace or the like with a single continuous jointless tube of semi-rigid heat conductive metal bent in a serpentine shape incorporating elongated substantially parallel horizontal legs fixed to respective ones of a plurality of horizontal aluminum fins directly opposing the stove or furnace firebox wall, the serpentine tube further having integral bends at the ends of the fins and by which the legs of the serpentine tube are integrally joined in series to permit water to be heated to flow back and forth across the face of the stove. Cover means overlie the fins and serpentine tube to trap heat supplied by the firebox in the region of the fins and tubes.